1. Field of the Invention
The present invention may be directed to a process for starting a motor vehicle having a braking system that obtains brake actuation energy at least partially from brake energy storage devices. A charging state for each brake energy storage device may be checked when the motor vehicle is started. The invention may also be directed to a motor vehicle having a braking system that obtains brake actuation energy at least partially from brake energy storage devices, and having a testing device for checking the charging state of the brake energy storage devices.
2. Discussion of Background Information
Braking systems, particularly those utilized in passenger motor vehicles, have been developed which are of the brake-by-wire type. In braking systems of this kind, an amount of braking desired by the driver is translated from a foot force exerted on a brake pedal, and the exerted foot force is detected by a sensor and converted into an electrical signal. The signal is transmitted to brake actuators associated with a particular wheel of the motor vehicle, and each brake actuator exerts a braking force on the vehicle wheel with the assistance of an electromotor. Thus, the brake actuation energy required for performing a braking procedure is not mechanically supplied, as in conventional brake systems, but is electrically supplied. Accordingly, electrical brake energy storage devices must be supplied to enable the supply of electrical energy to the braking system to perform the desired braking procedure. In this regard, part of the energy supplied to the braking system can come from the normal wiring system of the vehicle and another part of the supplied energy, which would overload the normal wiring system, comes from separate brake energy storage devices. A brake system substantially similar to the above-described system is described in the Applicants' German Patent Application No. 195 40 265.0, the disclosure of which is incorporated by reference. Alternatively, the electrical energy required for the brake system may be exclusively supplied by a separate brake energy storage device. Thus, a sufficient charging state of the separate brake energy storage devices is particularly important to the safety of the braking system. For this reason, the charging state of the brake energy storage devices has to be continuously checked, particular when the vehicle is started.
A brake system with electrically controllable brake devices has been disclosed in DE 35 02 100 A1. The system includes a first energy storage device for normal operation and a second energy storage device for emergency operation. Both brake energy storage devices are associated with a voltage monitoring device to continuously check the charging state of the brake energy storage devices. If an insufficient charging state level (amount) is detected in the first energy storage device to perform normal operation, then a change-over device switches the system over to the second energy storage device for emergency operation. The first energy storage device is switched over to be charged by a generator. The changeover to emergency operation is optically or acoustically indicated to the driver of the vehicle with a signal transmitter.
The charging state of the first energy storage device is also checked when the vehicle is started. When the charging state is found insufficient, the above-mentioned signal transmitter indicates this state to the driver and the braking system is then switched over to the second energy storage device to utilize its energy supply. If the second energy storage device has an insufficient charging state, then the signal transmitter indicates this state to the driver.
According to DE 35 02 100 A1, an additional safety is produced by checking the charging state of the brake energy storage device of the braking system and by providing a second energy storage device. The process for starting a vehicle disclosed in the above-noted document relates to a passive process, since the charging state of the energy storage device for normal operation or the charging state of the energy storage device for emergency operation is only optically or acoustically indicated to the driver. The safety of the vehicle, therefore, is not actively increased by this starting process.